K. Schwarzschild's problem in radiation transfer theory

We solve exactly the problem of a finite slab receiving an isotropic radiation on one side and no radiation on the other side. This problem - to be more precise the calculation of the source function within the slab - was first formulated by K. Schwarzschild in 1914. We first solve it for unspecified albedos and optical thicknesses of the atmosphere, in particular for an albedo very close to 1 and a very large optical thickness in view of some astrophysical applications. Then we focus on the conservative case (albedo = 1), which is of great interest for the modeling of grey atmospheres in radiative equilibrium. Ten-figure tables of the conservative source function are given. From the analytical expression of this function, we deduce 1) a simple relation between the effective temperature of a grey atmosphere in radiative equilibrium and the temperature of the black body that irradiates it, 2) the temperature at any point of the atmosphere when it is in local thermodynamical equilibrium. This temperature distribution is the counterpart, for a finite slab, of Hopf's distribution in a half-space. Its graphical representation is given for various optical thicknesses of the atmosphere.Comment: 21 pages, 2 figures, JQSRT, accepted 16 May 200

Short-lived isomers in Po-192 and Po-194

Isomeric states in Po194 and Po192 were studied at the velocity filter SHIP. The isotopes were produced in the fusion-evaporation reactions Pr141(Fe56, p2n)Po194 and Sm144(V51, p2n)Po192. Several new γ-ray transitions were attributed to the isomers and γ−γ coincidences for both isomers were studied for the first time. The 459-keV transition earlier, tentatively proposed as de-exciting the isomeric level in Po194, was replaced by a new 248-keV transition, and the spin of this isomer was reassigned from (11−) to (10−). The de-excitation of the (11−) isomeric level in Po192 by the 154-keV transition was confirmed and a parallel de-excitation by a 733-keV (E3) transition to (8+) level of the ground-state band was suggested. Moreover, side feeding to the (4+) level of the ground-state band was proposed. The paper also discusses strengths of transitions de-exciting 11− isomers in neighboring Po and Pb isotopes